Electrically heated bedcover with thermostatless overheat protection circuit and separate comfort control

ABSTRACT

An electrically heated bedcover wherein the generation of heat upon flow of electrical current through an electrical heating element is controlled, in response to variations in ambient temperature affecting the comfort of a user of the bedcover, by a comfort control circuit while continuance of any unsafe localized overheat condition is prevented by an overheat protection circuit which is physically separate from the comfort control circuit. By such separation, an electrically heated bedcover having a gate controlled semiconductor switch included in a thermostatless overheat protection circuit is adapted for cooperation with a comfort control circuit which also has utility with other types of electrically heated bedcovers.

United States Ratent Mills et a1.

[54] ELECTRICALLY HEATED BEDCOVER WITH THERMOSTATLESS OVERHEATPROTECTION CIRCUIT AND SEPARATE COMFORT CONTROL [72] Inventors: Edwin R.Mills, Raleigh; Ernest L.

Elmore, Smithfield, both of N.C.

[73] Assignee: Fieldcrest Mills, Inc., Eden, N.C.

[22] Filed: Feb. 26, 1971 [21] Appl. No.: 119,104

[52] US. Cl. ..2l9/212, 219/501, 219/529, 219/549 [51] Int. Cl. ..H05b1/00 [58] Field of Search ..219/21 1, 212, 527, 529, 549, 219/501;128/379, 402; 5/343 Aug. 8, 1972 3,437,792 4/1969 Lauck ..2l9/212 X3,108,175 10/1963 Zartman et a1. ..212/212 X 3,543,005 11/1970 Kelemen..219/212 X 2,959,662 1l/l960 Crowley et al ..2l9/212 PrimaryExaminer-C. L. Albritton Attorney-Parrott, Bell, Seltzer, Park & Gibson[57] ABSTRACT An electrically heated bedcover wherein the generation ofheat upon flow of electrical current through an electrical heatingelement is controlled, in response to variations in ambient temperatureaffecting the comfort of a user of the bedcover, by a comfort controlcircuit while continuance of any unsafe localized overheat condition isprevented by an overheat protection circuit which is physically separatefrom the comfort control circuit. By such separation, an electricallyheated bedcover having a gate controlled semiconductor switch includedin a thermostatless overheat protection circuit is adapted forcooperation with a comfort control circuit which also has utility withother types of electrically heated bedcovers.

8 Claims, 4 Drawing Figures '1 ELECTRICALLY HEATED BEDCOVER WITHTHERMOSTATLESS OVERHEAT PROTECTION CIRCUIT AND SEPARATE COMFORT CONTROLComfort and safety of users of electrically heated bedcovers haveheretofore been accommodated by using comfort control means permitting auser to warm the bedcover to varying degrees felt necessary for comfortand overheat protection means for precluding the continuance of alocalized overheating condition otherwise possibly leading to injury tothe user. In one conventional arrangement, overheat protection isprovided by a plurality of normally closed, bimetallic thermostaticswitches disposed throughout the heated area of the bedcover andelectrically connected in series with an electrical resistance heatingelement in the l bedcover. Comfort control is provided by an ambienttemperature responsive control circuit including a bimetallicthermostatic switch electrically connected in series with the electricalresistance heating element, adjusted by a user and responsive to heatgenerated by a compensating heater. Such an arrangement for anelectrically heated bedcover typically mounts the ambient temperatureresponsive control circuit in a housing to be positioned on a bedsidetable or the like, with electrical connection between the ambienttemperature responsive control and the electrical resistance heatingelement being through an elongate cable.

Such previously used electrically heated bedcover arrangements have beenwidely adopted by bedcover manufacturers and, through the economiespossible by mass production, have become relatively inexpensive toproduce. However, such an arrangement is subject to a number ofdeficiencies apparent to users of such electrically heated bedcovers. Inparticular, the bimetallic thermostatic switches used for overheatprotection are relatively bulky, and are apparent in the bedcover. Thetextile blanket shell or other bedcover is subject to more rapid wear atthe location of a thermostat than at other locations, leading to morerapid deterioration in the appearance of the bedcover.

It has been proposed that overheat protection means in electricallyheated bedcovers be constructed to avoid these deficiencies of moreconventional bimetallic thermostatic switches, through use ofthermostatless sensing means for detecting the occurrence of an overheatcondition constructed as a pair of signal wires having a temperaturesensitive material therebetween. While such electrically heatedbedcovers have been successful, such arrangements are neither compatiblewith conventional ambient temperature responsive controllers nor asinexpensive to produce-as the aforementioned conventional arrangementdue to a requirement for multiple conductor cables to extend fromcircuitry in the bedcover to circuitry in a separate control housing.

It has now been recognized that significant economies can be realized,while taking advantage of the aesthetic and practical benefits ofthermostatless overheat protection circuit means as briefly mentionedabove, through the separation, in an electrically heated bedcover, ofcomfort control and overheat protection means. It is accordingly anobject of the present invention to separate, in an electrically heatedbedcover arrangement, the functions of comfort control and overheatprotection, in order that the comfort control circuitry may be madeoperable with a variety of bedcover arrangements while a thermostatlessoverheat protection circuit providing aesthetic and practical benefitsmay be employed if desired. In accomplishing this object of the presentinvention, an elongate, two conductor cable means is employed forelectrically connecting the comfort and overheat protection controlcircuitry, thereby reducing the expense incurred in manufacturing thecombination in accordance with the present invention.

Some of the objects and advantages of the invention having been stated,others will appear as the description proceeds, when taken in connectionwith the accompanying drawings, in which FIG. 1 is a perspective view ofan electrically heated bedcover in accordance with this invention;

FIG. 2 is a schematic illustration of ambient temperature responsivecontrol circuitry used in the bedcover arrangement of FIG. 1;

FIG. 3 is a view similar to FIG. 2 illustrating overheat protectioncircuitry used in the bedcover arrangement of FIG. 1; and

FIG. 4 is a perspective view of an alternative form of bedcover inaccordance with this invention.

The electrically heated bedcover of the present invention will bedescribed hereinafter with particular reference to the arrangementillustrated in FIGS. 1-3, with it being understood that the drawings andthe following description relate to an illustrative embodiment only andare to be construed broadly, rather than being considered as limitingthe present invention. An electrically heated bedcover in accordancewith the present invention comprises a bedcover generally indicated at10, a bedside comfort control housing 20, cable means 30 extendingbetween the comfort control housing 20 and the bedcover l0, and a powercord 40 by which the electrically heated bedcover arrangement may beconnected with a suitable source of alternating electrical current.Circuitry within the bedside control housing 20 and the bedcover 10, inaccordance with the present invention, is described with particularreference to F IGS. 2 and 3 wherein the bedcover 10 is schematicallyillustrated as comprising a textile blanket shell 11, an electricalresistance heating element means 12 disposed in and extending throughthe blanket shell 11, sensing means generally indicated at 14 fordetecting the occurrence of an overheat condition in the bedcover, andswitch means 15 for responding to the occurrence of an overheatcondition as disclosed more fully hereinafter. Within the housing 20 areprovided comfort control means operable between conductive andnon-conductive states and, in the illustrated embodiment, for varyingthe intervals of time during which successive complete cycles ofalternating electrical current are conducted through a bimetallicthermostatic switch 21 and a compensating heater 22.

In accordance with the present invention, the cable 30 is an elongatetwo conductor cable extending between and electrically connecting theheating element means 12 and the circuitry within the housing 20.Preferably, for convenience in laundering and storage, the cable 30terrrrinates, at an end remote from the housing 20, in a first plug 31which, together with a second plug 32 secured to the bedcover 10,comprises mating plug means for separably connecting the cable means 30and the heating element 12. It will be noted that the illustratedembodiment is of a bedcover having a single heated area rather than adual control blanket having two heated areas separately controlled. Inthe latter instance (not illustrated) three or four conductor cables maybe used in practicing the present invention, to provide correspondingtwo conductor cable means between cooperating controls and heated areas.

Where the mating plug means 31, 32 are connected, the switch means ofthe comfort control means is electrically connected in series with oneconductor of the cable means 30 and thereby placed in series connectionwith the heating element 12. Thus, operation of the switch betweenconductive and non-conductive states varies the conduction of cycles ofalternating electrical current through the heating element 12 forgenerating heat in the bedcover 10. The switch responds to ambientconditions by increasing the length of time for conduction through theswitch as ambient temperature decreases.

The sensing means 14 and switch means 15, briefly described hereinabove,cooperate with other circuit elements now to be described to provide athermostatless overheat protection means electrically interposed betweenthe cable means 30 and the heating element means 12 for modulating theaverage power of electrical current flowing therethrough. In particular,the switch means 15, in accordance with the present invention, is a gatecontrolled semiconductor switch such as a thyristor capable ofconducting both' positive and negative half-cycles of alternatingelectrical current. Such a gate controlled semiconductor switchtypically has first and second terminals for primary conduction ofelectrical current therethrough and a gate terminal to which gatingsignals are applied to control the portion of a cycle of alternatingcurrent conducted therethrough. By modulation of the phase relationshipof gating signals applied to the gate terminal, the average powerdelivered through the semiconductor switch may be varied.

In the circuitry of the present invention, the semiconductor switchmeans 15 is located at the blanket shell 11 and is electricallyconnected in series with the heating element means 12. Thus, uponmodulation of gating signals applied to the gate terminal of thesemiconductor switch means 15, the average power of electrical currentflowing through the heating element 12 is modulated.

In accordance with the present invention, sensing means 14 comprises apair of signal wires having a temperature sensitive electricallyconductive material disposed therebetween for varying conductancebetween the signal wires in accordance with the temperature of thesensing means 14. The sensing means 14 is disposed in the blanket shell11 in heat exchange relation with the heating element means 12, so as tobe responsive to the occurrence of a potentially unsafe localizedoverheating condition. Such conditions may occur, as is known, in theevent that the bedcover 10 becomes wadded or covered over with a heavybedspread or the like.

It is to be noted that a triggering capacitor C2, a resistor R and abreakdown triggering device D are electrically connected with the gateterminal of the semiconductor switch means 15. During normal operationof the circuitry of the present invention, gating signals pass throughthe sensing means 14 and a triggering device Din phase relation withcycles of alternating electrical current conducted through the comfortcontrol means trigger the semiconductor switch means 15 into conduction.such thatsubstantially full cycles of altemating electrical current arenormally conducted therethrough. In response to the occurrence of anoverheat condition, the effective values of the triggering circuit arechanged by a change in the dielectric characteristic between the signalwires of the sensing means 14, changing the phase relationship of gatingsignals applied to the semiconductor switch means 15 in such a way thatsignificantly less than full cycles of alternating electrical currentare conducted therethrough. The average power delivered through theheating element 12 is thus reduced, and continuance of the undesirableoverheating condition is avoided.

While the combination of a breakdown triggering device D and gatecontrolled semiconductor switch 15 is herein disclosed as a preferredarrangement, there are presently available commercial devices whichcombine these functions. One such device is the Quadrac, a brand offeredby ECC Corp., which combines the functions of triggering device andswitch in a single unit. In one operating embodiment of this invention,the component used is an ECC Q82 Quadrac.

In order to suppress radiation of radio frequency energy, the circuitryincludes a choke I and filter capacitors C1 and C3.

It is to be noted that, in the embodiment of FIGS. 2 and 3, thesemiconductor switch means 15 is mounted on a circuit board 33 withinthe second plug 32. An alternative embodiment, illustrated in FIG. 4,differs from the embodiment of FIG. 3 in that the semiconductor switchmeans 15 is mounted on a circuit board 33' within the blanket shell 11',but spaced from the second plug 32. In FIG. 4, elements which have beenmodified from those heretofore identified in FIGS. 1-3, but havingfunctions similar to those elements previously identified, areidentified by primed reference characters. Elements which are identicalin the embodiments of FIGS. 1-3 and FIG. 4 are identified by commonreference characters. The semiconductor switch means 15' of thealternative embodiment is mounted on a circuit board 33 located asindicated by the phantom line block, spaced from the second plug 32 andlocated near a hem of the blanket shell 11'.

As will be understood from the discussion hereinabove, the bedcover 10in accordance with the present invention is not subject to thedeficiencies heretofore noted in circumstances where overheat protectionis accomplished by bimetallic thermostatic switches electricallyconnected in series with the heating element disposed in a textileblanket shell. Instead, a distributed sensing means 14 is employed, topermit the textile blanket shell 1 1 to more closely approximate theappearance of a conventional unheated bedcover and to reduce thelikelihood of accelerated wear for the bedcover 10. Further, thisdesirable arrangement is accomplished without introducing multiconductorcable as the cable means 30 to extend between the housing 20 andbedcover l0, and without excessively complicating the comfort circuitrycontained within the housing 20. Instead, the housing 20 and cable means30 are constructed in a form which is widely applicable in connectionwith other, more conventional, bedcovers.

a generic and descriptive sense only and not purposes of limitation.

That which is claimed is:

1. An electrically heated bedcover comprising:

a bedcover,

electrical heating means in said bedcover for generating heat upon flowof electrical current therethrough, comfort control means separate fromsaid bedcover and operable between electrically conductive andnon-conductive states for controlling conduction of alternatingelectrical current therethrough, said comfort control means includingcompensating means responsive to ambient temperature conditions forincreasing conduction of alternating electrical current as ambienttemperature decreases,

elongate two conductor cable means extending between and electricallyconnecting said heating means and said comfort control means fordirecting electrical current conducted through said comfort controlmeans to flow through said heating means, said cable means having aterminal end remote from said comfort control means which is adapted forconnection with said heating means, and

overheat protection means electrically connected between said remote endof said cable means and said heating means for modulating the averagepower of electrical current flowing therethrough, said overheatprotection means including sensing means in said bedcover for detectingthe occurrence of an overheat condition and switch means located at saidbedcover for normally conducting substantially full cycles ofalternating electrical current and for responding to the occurrence ofan overheat condition by conducting significantly less than full cyclesof alternating electrical current.

2. An electrically heated bedcover according to claim 1 furthercomprising mating plug means for separably connecting said cable meansand said heating means said plug means including a first plug at aterminal end of said cable means and a second plug secured to saidbedcover, and further wherein said switch means of said overheatprotection means is disposed at said plug means.

3. An electrically heated bedcover according to claim 2 wherein saidswitch means is mounted within said second plug.

4. An electrically heated bedcover according to claim 1 wherein saidswitch means of said overheat protection means is mounted within saidbedcover.

5. An electrically heated bedcover according to claim 1 wherein saidcompensating means comprises a bimetallic thermostatic switchelectrically connected in series with one conductor of said cable meansand compensating heater means thermally couples to said thermostaticswitch for thermally biasing the same.

6. An electrically heated bedcover according to claim 1 wherein saidswitch means of said overheat protection means is a gate controlledsemiconductor switch and said sensing means comprises temperaturesensitive electrically conductive means disposed in said bedcover inheat exchange relation with said heating means and electricallyconnected with said semic0n ductor switch for controlling the portion ofa cycle of alternating electrical current conducted therethrough.

7. An electrically heated bedcover comprising: a blanket, electricalheating means in said blanket for generating heat upon flow ofelectrical current therethrough, a control housing separate form saidblanket, ambient temperature responsive control means in said housingfor responding to variations in room temperature affecting the comfortof a user of the bedcover, said control means including switch meansoperable between electrically conductive and non-conductive states forcontrolling conduction of electrical current through said control means,cable means extending between said housing and said blanket andelectrically connecting said heating means in series with said switchmeans, said cable means having a terminal end remote from said housingwhich is adapted for connection with said heating means, and overheatprotection means for reducing the average power delivered by electricalcurrent flowing through said heating means, said overheat protectionmeans including gate controlled semiconductor switch means located atsaid blanket and electrically connected between said remote end of saidcable means and said heating means and sensing means in said blanket andoperatively connected to said semiconductor switch means for detectingthe occurrence of an overheat condition and for modulating conductanceof current through said semiconductor switch means in the event anoverheat condition occurs. 8. An electrically heated bedcovercomprising: a textile blanket shell, electrical heating means in saidblanket shell for generating heat upon flow of electrical currenttherethrough, ambient temperature responsive control means spaced fromsaid blanket shell for responding to variations in room temperatureaffecting the comfort of a user of the bedcover, said control meansincluding switch means operable between electrically conductive andnon-conductive states for controlling conduction of electrical currentthrough aid control means, cable means extending between said controlmeans and said blanket shell and electrically connecting said heatingmeans in series with said switch means, said cable means having aterminal end remote from said control means which is adapted forconnection with said heating means, and overheat protection means forreducing the average power delivered by electrical current flowingthrough said heating means, said overheat protection means includinggate controlled semiconductor switch means located intermediate saidblanket shell and said remote end of said cable means and electricallyconnected in series with said heating means and further includingsensing means in said blanket shell and operatively connected to saidsemiconductor switch means for detecting the occurrence of an overheatcondition and for modulating conductance of current through saidsemiconductor switch means in the event an overheat condition occurs.

1. An electrically heated bedcover comprising: a bedcover, electricalheating means in said bedcover for generating heat upon flow ofelectrical current therethrough, comfort control means separate fromsaid bedcover and operable between electrically conductive andnon-conductive states for controlling conduction of alternatingelectrical current therethrough, said comfort control means includingcompensating means responsive to ambient temperature conditions forincreasing conduction of alternating electrical current as ambienttemperature decreases, elongate two conductor cable means extendingbetween and electrically connecting said heating means and said comfortcontrol means for directing electrical current conducted through saidcomfort control means to flow through said heating means, said cablemeans having a terminal end remote from said comfort control means whichis adapted for connection with said heating means, and overheatprotection means electrically connected between said remote end of saidcable means and said heating means for modulating the average power ofelectrical current flowing therethrough, said overheat protection meansincluding sensing means in said bedcover for detecting the occurrence ofan overheat condition and switch means located at said bedcover fornormally conducting substantially full cycles of alternating electricalcurrent and for responding to the occurrence of an overheat condition byconducting significantly less than full cycles of alternating electricalcurrent.
 2. An electrically heated bedcover according to claim 1 furthercomprising mating plug means for separably connecting said cable meansand said heating means said plug means including a first plug at aterminal end of said cable means and a second plug secured to saidbedcover, and further wherein said switch means of said overheatprotection means is disposed at said plug means.
 3. An electricallyheated bedcover according to claim 2 wherein said switch means ismounted within said second plug.
 4. An electrically heated bedcoveraccording to claim 1 wherein said switch means of said overheatprotection means is mounted within said bedcover.
 5. An electricallyheated bedcover according to claim 1 wherein said compensating meanscomprises a bimetallic thermostatic switch electrically connected inseries with one conductor of said cable means and compensating heatermeans thermally couples to said thermostatic switch for thermallybiasing the same.
 6. An electrically heated bedcover according to claim1 wherein said switch means of said overheat protection means is a gatecontrolled semiconductor switch and said sensing means comprisestemperature sensitive electrically conductive means disposed in saidbedcover in heat exchange relation with said heating means andelectrically connected with said semiconductor switch for controllingthe portion of a cycle of alternating electrical current conductedtherethrough.
 7. An electrically heated bedcover comprising: a blanket,electrical heating means in said blanket for generating heat upon flowof electrical current therethrough, a control housing separate form saidblanket, ambient temperature responsive control means in said housingfor responding to variations in room temperature affecting the comfortof a user of the bedcover, said control means including switch meansoperable between electrically conductive and non-conductive states forcontrolling conduction of electrical current through said control means,cable means extending between said housing and said blanket andelectrically connecting said heating means in series with said switchmeans, said cable means having a terminal end remote from said housingwhich is adapted for connection with said heating means, and overheatprotection means for reducing the average power delivered by electricalcurrent flowing through said heating means, said overheat protectionmeans including gate controlled semiconductor switch means located atsaid blanket and electrically connected between said remote end of saidcable means and said heating means and sensing means in said blanket andoperatively connected to said semiconductor switch means for detectingthe occurrence of an overheat condition and for modulating conductanceof current through said semiconductor switch means in the event anoverheat condition occurs.
 8. An electrically heated bedcovercomprising: a textile blanket shell, electrical heating means in saidblanket shell for generating heat upon flow of electrical currenttherethrough, ambient temperature responsive control means spaced fromsaid blanket shell for responding to variations in room temperatureaffecting the comfort of a user of the bedcover, saId control meansincluding switch means operable between electrically conductive andnon-conductive states for controlling conduction of electrical currentthrough aid control means, cable means extending between said controlmeans and said blanket shell and electrically connecting said heatingmeans in series with said switch means, said cable means having aterminal end remote from said control means which is adapted forconnection with said heating means, and overheat protection means forreducing the average power delivered by electrical current flowingthrough said heating means, said overheat protection means includinggate controlled semiconductor switch means located intermediate saidblanket shell and said remote end of said cable means and electricallyconnected in series with said heating means and further includingsensing means in said blanket shell and operatively connected to saidsemiconductor switch means for detecting the occurrence of an overheatcondition and for modulating conductance of current through saidsemiconductor switch means in the event an overheat condition occurs.